The present invention relates to a method and apparatus for molding a receptacle fitted with a covering label.
The technical field of the invention is that of molding a receptacle out of plastics material.
The invention applies particularly to the method of manufacturing a plastic material package covered by a label over a portion of at least one face, in particular a portion of an outside face; more particularly, The invention relates to packages such as boxes, pots, bottles, or tubes (e.g. for receiving gases, liquids, or pastes, in particular foodstuffs such as yogurt) where the substantially one-piece structure body can have a bottom-forming wall and one or more side walls e.g. extending over a surface of revolution about an axis perpendicular to the plane of the bottom, such as a cylinder or a truncated cone; the invention applies more particularly, to such packages or receptacles that are of relatively small size, i.e. in which the largest dimension is less than one meter, e.g. of the order of 5 cm to 30 cm.
The invention applies to this type of package as obtained by molding, generally injection molding of plastics materials, in a mold that has at least two portions that move relative to each other: a female portion or xe2x80x9cmatrixxe2x80x9d that has at least one cavity corresponding to the outside shape of the receptacle that is to be manufactured, and a male portion or xe2x80x9ccorexe2x80x9d that has at least one projecting portion corresponding to the inside face of the receptacle that is to be manufactured.
The invention also applies to such packages where the label is secured to the plastics material body by adhesion obtained by molding over the label, i.e. by inserting the label into the mold prior to the plastics material that is to form the body of the package itself being introduced into the mold; The label is of a shape that matches the final shape of the package, and it is generally obtained from a sheet of paper or plastics material such as polypropylene in particular, which is cut out to the desired shape and covered in patterns by any conventional printing method.
In general, prior to each molding cycle, a plane label (i.e. a label that is disposed flat) is transferred to a mold, e.g. by a clamp and/or suction cup system, generally from a magazine that contains a stack of labels, and there are two main techniques for doing this;
A first technique uses a transfer tool (or mandrel) of a shape that is suitable for penetrating into the inside of the mold matrix. The initially plane label is placed around the mandrel and is simultaneously deformed so as to take up the outside shape of the mandrel; The label deformed in this way is held in contact with the outside face of the mandrel by applying electrostatic forces or by establishing suction (by sucking air) at the outside face of the transfer mandrel, i.e. beneath the label; After the transfer mandrel carrying the label has been moved from the storage magazine to the inside of the cavity of the matrix, the means for holding the label on the matrix (electrostatically or by suction) are deactivated; the label tends to return to its initial plane shape because of the relative stiffness of the material(s) from which it is made, so it separates from the transfer mandrel and comes into close contact with at least a portion of the faces of the cavity-forming female portion of the mold; After the mandrel has been removed from the cavity and the core (or punch) has penetrated therein, plastics material is introduced into the space between the core and the matrix and also into the space between the core and the label, thus causing the label to be pressed against the walls of the matrix under drive from the forces exerted thereon by the injected plastics material.
Patent FR 2 627 744 (Gizeh Sarl) describes another technique for automatically manufacturing a receptacle with a covering label in which labels are transferred from the magazine to the mold by two rotary clamps which roll the label up into the form of a cornet, the label as rolled up in this way being taken hold of by a transfer clamp which inserts the label in the mold matrix. The rotary clamps roll the label up into a cornet by causing the free ends of the label to overlap, and the label rolled up into the shape of a cornet is then taken hold of where its free ends overlap by the transfer clamp which inserts the rolled-up label into the matrix.
Those known techniques have the drawback of generally requiring the matrix to be fitted with suction means for holding the label in place in the cavity until the plastics material is injected.
Another drawback of methods in which a transfer mandrel is used is the lack of accuracy with which the label is positioned on the mandrel, and the way the label deforms during and after being put into place on the transfer mandrel; This drawback is not resolved by the above-mentioned French patent; consequently, the positioning of the label in the mold cavity lacks precision, and that leads to receptacles being manufactured that are defective because the label is in the wrong position.
Another major drawback is that accurate handling and positioning of the Label by clamps or suction cups is not possible when the label is very thin, e.g. having a thickness of less than 80 microns; Labels that are that thin are fragile and difficult to handle, and they tend to deform and/or move in uncontrolled manner under the effect of their own weight or under the effect of the mechanical stresses caused by mechanical contact between the labels and the handling members (even though attempts are made to minimize those forces), or indeed under the effect of electrostatic forces; In addition, their small thickness gives rise to small stiffness and that can be insufficient to enable the label to separate spontaneously from the mandrel or other transfer means, which can prevent positioning and holding in the cavity of the matrix or which can at least make it more difficult, or indeed which can require holding forces to be applied thereto by auxiliary means such as electrostatic means or pneumatic means (operating by suction).
Unfortunately, it is advantageous in some cases, in particular for the purpose of keeping down costs, to use labels having thickness of the order of 10 microns to 40 microns.
The object of the invention is thus to propose an improved method and apparatus for automatically manufacturing packages or receptacles that include a label.
An essential object of the invention is to provide such methods and corresponding apparatuses for implementing them to make it possible to provide a package manufacturing cycle time that is as short as possible; the time required for injection (which can lie in the range of a few seconds to a few minutes depending essentially on the dimensions of the package) is penalized (i.e. lengthened) by the time required for transferring the label into the mold, which time can be greater than 5 seconds when a mandrel is used.
From this point of view in particular, the system for transferring labels from the magazine to the mold by means of members such as mandrels or clamps not only leads to mechanical structures that are complex and expensive (and which also need to be adapted to the shape of each label and thus need to be interchangeable in order to manufacture receptacles in a range of shapes or sizes), but they also increase cycle time and slow down manufacturing throughput.
For example, transfer devices which have electrostatic means for holding the label on a mandrel suffer from a drawback which is due to the use of electrical voltages for causing labels to adhere by the electrostatic effect on the receiving portions of the transfer means, thereby giving rise to electromagnetic disturbances to the operation of the apparatus, and they are also incompatible with thin films.
In addition, known transfer devices do not make it possible to position the free edges of the label so that they are accurately in register, i.e. edge to edge, or they are poor at so doing, thus giving rise to a resulting receptacle suffering from poor appearance and which is fragile.
The problems mentioned are made worse when it is desired to use molds that have a plurality of cavities; since the use of such molds gives rise to additional constraints in design (and use) because of the small amount of space left free between two consecutive cavities through which a label can be transferred into the mold, thereby leading to complex transfer systems being designed, and usually to the detriment of the time required to transfer a label from the magazine to the mold cavity.
In a first aspect, the invention consists in forming a label so that it takes up its final shape or at least an intermediate shape that is not planar, i.e. a shape that is three-dimensional or that occupies volume, in joining together at least two free edges of the label (or indeed two portions thereof, e.g. two small xe2x80x9cspotxe2x80x9d zones of the label that are situated close to the free edges thereof). This is accomplished preferably by heat-sealing or adhesive so that the edges are either in an edge-to-edge configuration or else have an overlap margin, and then in placing the label that has been pre-shaped in this way on a male portion (or core) of the mold.
In other words, the invention consists in proposing a method of molding a receptacle fitted with a label covering the receptacle, in which the label is rolled up before it is inserted into the mold, the method being characterized in that the label is stabilized in its final shape or in an intermediate (non-planar) shape, e.g. a shape in which it is rolled into a cylinder or a truncated cone, by joining together at least two portions of the label (preferably by adhesive or by heat-sealing), and then the stabilized shaped or pre-shaped (e.g. rolled) label is engaged on a male portion (or core) of the mold, after which the core is brought up to the matrix with the core serving as a support for the label. The plastics material is injected.
Because the label is put into place on the core rather than in the matrix, manufacturing cycle time can be reduced, for several reasons, and in some cases their effects can be cumulative.
First it is possible to put the label into place in xe2x80x9cnon-criticalxe2x80x9d time, i.e. simultaneously with the operation of withdrawing the receptacle manufactured during a previous manufacturing cycle from the matrix.
Second it is also possible to engage the label (on the core) part of the way only by means of a first transfer member, and then to continue the engagement operation by means of a second transfer member; this final engagement operation can consist merely in moving an abutment linearly in translation along a longitudinal axis of the core (the axis of revolution for a frustoconical core) in order to push the label along said axis; This operation therefore avoids any need to activate or deactivate mechanical, pneumatic, or electrostatic means for gripping the label by the transfer member and/or for holding the label on the core; in addition, return (along a return axis) of the transfer members to take hold of a new pre-shaped label does not require the transfer members to perform a disengagement movement relative to the core along an axis other than the return axis.
Third this saving in time together with accurate positioning of the label on the core is also favored by the fact that the pre-formed label is stiffer, at least in one of the three dimensions, and therefore less liable to become deformed, than is a flat sheet constituting a label blank, i.e. a label that has not been pre-shaped and that has not been joined together; Because of this xe2x80x9cintrinsicxe2x80x9d stiffness of a shaped label, which is greater than the stiffness of a flat label sheet (not yet joined together), it is possible to use labels of reduced thickness.
Because it is possible to omit electrostatic means for holding the label on the core (or punch), it is possible to place the pre-shaped label on male mold portions that are very close together in a multi-cavity mold; This possibility is also favored by the fact that the size of the pre-formed label (in at least one of the three dimensions) is smaller than the size of a xe2x80x9cflatxe2x80x9d label blank.
In multi-cavity molds, the space available between two adjacent cavities and/or the pitch at which the cavities are spaced is generally smaller than the dimensions of the label when flat; under such circumstances, there is specifically no question of using electrostatic forces for rolling a flat label around a core.
In preferred embodiments of the invention, the pre-shaped label is deformed and/or folded so as to flatten it, thereby enabling it to be stored flat. The previously shaped and flattened label is then again deformed and/or opened or expanded, e.g. by blowing, thereby giving it again a shape that is close to its final shape as previously imparted thereto, and the reshaped label is transferred into the mold by being deposited on the core.
In other words, the label as previously rolled-up (or shaped) and joined-together (via at least two edge zones) and then flattened is stored flat and/or in a stack in a magazine. The label is then extracted from the magazine, and then caused to go from its rolled-up and flattened shape (or configuration) to a rolled-up and non-flattened configuration, preferably by being expanded by blowing.
To transfer the label into the mold, the pre-shaped label (rolled up and expanded) is placed or engaged (preferably in part only) on a mold core or punch, and the final positioning of the label around the core is performed by a thrust member (such as an actuator) which is movable relative to the transfer member (such as an actuator); This makes it possible to reduce the total cycle time required to manufacture the receptacle by enabling the transfer member(s) to move back towards the magazine preferably in a single direction (or axis) only, since there is no need to disengage the thrust member.
During the operation of shaping or rolling up the label prior to storing it flat, the two free edges of the label are joined together by adhesive or heat-sealing, either with the two free edges overlapping or else without overlap, i.e. edge to edge.
The labels used are made of paper, polypropylene, polyethylene, PVC, or ABS, having a thickness of not more than 80 microns, e.g. a thickness of not more than 50 microns; and
The total time required to transfer a label from a ready position outside the mold to a position where it is installed on the core, and including the return time, can be less than or equal to 5 seconds, preferably less than or equal to 3 seconds, e.g. about 1 to 2 seconds.
In another aspect, the invention consists in providing apparatus for molding a receptacle and for inserting a covering label into the mold, the apparatus being characterized in that it includes means for transferring and/or depositing a pre-shaped label on a male mold portion, the pre-shaped label having two zones (or edges) that have been previously joined together.
In preferred embodiments, the apparatus includes;
a storage magazine or means for storing rolled-up; shaped, and flattened or folded labels flat and/or in a stack; and/or
The shaping means, preferably operating by expanding a label from a rolled-up and flattened state (or shape) to a rolled-up and non-flattened state (or shape); and/or
means for expanding a rolled-up and flattened label by blowing, which means preferably include a plurality of nozzles pointing in different directions;
In the alternative, expansion can be obtained by radially deploying a mechanical hinged structure which pushes back the side walls of the label from the inside;
The apparatus may further include at least one means such as a suction cup, for pneumatically taking hold of a label by making contact with an outside face of the shaped and expanded label;
The apparatus may have means for transferring the label as extracted from the magazine and as expanded from the magazine to the mold and for placing it on the core, and preferably the apparatus includes distinct means for pushing against a label that has previously been engaged in part around the core.
The apparatus may include a magazine for storing a stack of labels fitted with means enabling labels (that have already been shaped, joined-together, and flattened) to be introduced to the top of the stack, The magazine can be fitted with means situated in the bottom portion of the stack and enabling shaped, joined-together, and flattened labels to be extracted therefrom (preferably one by one); and
the means for transferring the expanded label can include a plurality of gripping means that operate by making contact with the outside face of the label, such as suction cups.